I was in the same boat just after the 7Dii came out as I wanted an upgrade for my 7D. I chose the 1Div after trying both and have been very happy with it. I sold the 7D after but ended up getting another shortly after as I needed 2 bodies for football. I then picked up a 7Dii
second hand and sold the 7D. Having had both the 1Div and 7Dii for over a year I can say they complement each other very well but are better at different things and both mine get about the same amount of use.
Most wildlife and birds the 7Dii wins with the extra x.3 of reach, quieter and silent shutter option (1Div is very noisy), being able to program a button for +1/=2 EV when in M is supper useful for birds in flight, lighter to carry without a grip (I walk my dogs with it and a 150-600C quite often) it will also produce usable files at ISO12,800. Auto focus takes a bit of getting used to for moving subjects.
I do a fair bit of dragonflies in flight and the 1Div is my first choice as the noise is better between ISO800 to ISO1600 where the 7Dii starts to take over, it is heavier but this almost helps when following them.
For motorsport and football I will take the 1Div as it never fails to deliver, it is so simple to use, AF seems to just work better and faster, battery goes on for ever, it is more robust, not afraid of rain, hit rate is better.
Equestrian. Rare for me but I have too occasionally I will reluctantly take the 7Dii only because the shutter on the 1Div is so loud and has spooked horses doing dressage.
Landscape either work though the 1Div does produce lovely files so would just edge ahead.
Lenses used on both and work really well 24-105L, 70-200f2.8ii, Sigma 120-300s, Sigma 150-600c and Canon 300f4 and 500f4
Whilst owning the 1Div I have also owned a 5Dii and 5Diii both were sold as the 1Div seemed to do everything better.
If I had to sell one it would be a very difficult choice and one of the reasons I have not tried a 1Dxii, 5Div or Sony A9.